Mechanical combing or brushing to unravel nanofibers

A simple but non-precise method to loosen the fibers in the membrane to give a 3D profile is by mechanical combing or brushing [Shim et al 2010]. Through the mechanical action of combing or brushing, fibers can be separated from one another with repeated but gentle brushing. To produce an open fibrous structure with good morphology through brushing, the quality of the fiber mat has to be good. That means thin fibers and smooth mat with no obvious adhesions or beads. Zeng et al (2021) demonstrated the importance of fiber mat quality for the opening process. Any connected fiber junctions due to wet fibers or solution droplets fusing the fibers will result in tearing defects. Larger diameter fibers will also cause some tearing and bundling of fibers during the opening treatment. To achieve uniform and best fluffiness, the fibers should be of low diameter with no obvious adhesions or beads. An advantage of this method is its simplicity to "open up" the nanofibers. However, the difficulty is in creating a consistent three-dimensional structure with uniform expansion throughout the membrane during the unraveling process. It is also likely that this process will result in multiple fiber breakages.

Effect of opening treatment of fiber mats with different shapes. (a) Fiber mat with lots of lumps before opening treatment. (b) Fiber mat composed of thick fibers. (c) Fiber mat with good fiber quality [Zeng et al 2021].